Calculate sizes of all IndexDB database and tables

get_indexdb_sizes.js

var getTableSize = function (db, dbName) {
    return new Promise((resolve, reject) => {
        if (db == null) {
            return reject();
        }
        var size = 0;
        db = event.target.result;
        var transaction = db.transaction([dbName])
            .objectStore(dbName)
            .openCursor();

        transaction.onsuccess = function (event) {
            var cursor = event.target.result;
            if (cursor) {
                var storedObject = cursor.value;
                var json = JSON.stringify(storedObject);
                size += json.length;
                cursor.continue();
            } else {
                resolve(size);
            }
        }.bind(this);
        transaction.onerror = function (err) {
            reject("error in " + dbName + ": " + err);
        }
    });
};

var getDatabaseSize = function (dbName) {
    var request = indexedDB.open(dbName);
    var db;
    var dbSize = 0;
    request.onerror = function (event) {
        alert("Why didn't you allow my web app to use IndexedDB?!");
    };
    request.onsuccess = function (event) {
        db = event.target.result;
        var tableNames = [...db.objectStoreNames];
        (function (tableNames, db) {
            var tableSizeGetters = tableNames
                .reduce((acc, tableName) => {
                    acc.push(getTableSize(db, tableName));
                    return acc;
                }, []);

            Promise.all(tableSizeGetters)
                .then(sizes => {
                    console.log('--------- ' + db.name + ' -------------');
                    tableNames.forEach((tableName, i) => {
                        console.log(" - " + tableName + "\t: " + humanReadableSize(sizes[i]));
                    });
                    var total = sizes.reduce(function (acc, val) {
                        return acc + val;
                    }, 0);

                    console.log("TOTAL: " + humanReadableSize(total))
                });
        })(tableNames, db);
    };
};

var humanReadableSize = function (bytes) {
    var thresh = 1024;
    if (Math.abs(bytes) < thresh) {
        return bytes + ' B';
    }
    var units = ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
    var u = -1;
    do {
        bytes /= thresh;
        ++u;
    } while (Math.abs(bytes) >= thresh && u < units.length - 1);
    return bytes.toFixed(1) + ' ' + units[u];
};

var printIndexDBSizes = function () {
    indexedDB.databases().then(v => v.reduce((acc, cur) => (acc.push(cur.name), acc), []))
        .then(databaseNames => {
            var dbName;
            for (var i = 0; i < databaseNames.length; i++) {
                dbName = databaseNames[i];
                getDatabaseSize(dbName);
            }
        })
};

//usage
printIndexDBSizes();